1. Field of the Invention
The present invention relates to keyboards which supports N-key rollover technology.
2. Description of the Related Art
A ghost key (phantom key) is a phenomenon which commonly occurs with traditional keyboards, wherein some data is not inputted, even after the pressing of several keys.
Keys on a keyboard with ghost key phenomenon are usually arranged in a keyboard matrix. By looking up a keyboard code table based on the column data and row data of the keyboard matrix, the keyboard controller can locate the keys pressed by a user and output data. There are usually 16 column lines and 8 row lines on a printed circuit board of a mechanical keyboard. The column lines and the row lines intersect into 128 points, and each of the points represents a key (most keyboards have a total of 103 keys). Therefore, when a user presses a key, the keyboard controller scans the keyboard matrix and locates the pressed key. FIGS. 1A-1D show a simplified 2×2 keyboard matrix (having four intersected points for representing four keys “Q”, “W”, “A” and “S”, respectively) for illustrating how the keyboard controller determines the column and row data of a key.
In FIG. 1A, since the columns C1 and C2 and the rows R1 and R2 are not conducting, it can be determined that all of the four keys are not being pressed. In FIG. 1B, the user only presses the key “Q”. Since when scanning the column C1, the row R1 is conducting and the row R2 is not conducting, it can be determined that the intersected point of the column C1 and the row R1 (i.e., key “Q”) is being pressed but the intersected point of the column C1 and the row R2 (i.e., key “A”) is not being pressed. Since when scanning the column C2, the row R1 and the row R2 are both not conducting, it can be determined that the intersected points of the column C1 and the rows R1 and R2 (i.e., keys “W” and “S”) are not being pressed. Similarly, the keyboard controller in FIG. 1C can easily determine that two keys “Q” and “S are being pressed by the user. In FIG. 1D, although the user only presses three keys “Q”, “W” and “A”, since when scanning columns C1 and C2 it can be determined that both rows R1 and R2 are conducting, the keyboard controller may wrongly determine that there are four keys being pressed at the same time (including the key “S” which is not being pressed), thus producing “the ghost key”. In order to prevent this phenomenon, the keyboard controller usually neglects the third pressed key and only outputs the first and the second pressed key. This is the so called “two-key rollover” manner.
It is not ideal for a keyboard to only support two-key rollover, because it may cause problems with word processing and game playing. Therefore, the prior art also uses N-key rollover (NKRO) technology to overcome the mentioned defects. Many keyboard manufacturers assert that their keyboards support NKRO, but they actually don't; especially for keyboards with the USB interface (this type of keyboard can merely output any six keys excluding auxiliary keys such as “Shift”, “Ctrl” and “Alt”). Some keyboards with USB interfaces can support NKRO, but only for particular operating systems (OS).